1. Field of the Invention
The present invention relates to a method for adjusting the gram load of the suspension.
2. Background of the Invention
Head suspensions are commonly used in magnetic disk drives to support the magnetic read/write heads in close proximity to the rotating magnetic disks. The well known and widely used Watrous-type suspensions such as that disclosed in the Blaeser et al. U.S. Pat. No. 5,198,945 include a load beam having a mounting region or base plate at a proximal end, a flexure on a distal end, a relatively rigid region adjacent to the flexure and a spring region between the base plate and rigid region. An air-bearing, slider which includes the magnetic head is mounted to the flexure. The load beam and flexure are typically manufactured by etching and forming a thin stainless steel sheet. The slider is then adhesively bonded to the flexure.
During operation of the disk drive, typically the slider does not touch the rotating disk. Rather, the force of the air rotating with the disk causes the slider to fly at a microscopic distance known as the "fly height" above the disk. The suspension urges the slider toward the disk with a force known as the gram load to counteract the slider-generated air-bearing forces and maintain the proper fly height.
The gram load is established during the suspension manufacturing operation. Techniques for adjusting suspension gram loads are well known and disclosed, for example, in the Schones et al. U.S. Pat. No. 5,297,413. One common gram load adjustment technique involves mechanically bending the suspension at the spring region to increase (i.e., to upgram) or decrease (i.e., to downgram) the gram load. Another technique known as "light adjustment" involves the application of heat to the spring region. Heat relieves mechanical stresses in the spring region and lowers the gram load. During suspension manufacture the gram loads are adjusted to predetermined tolerances to provide the proper fly height. Excessive fly height can impair the ability of the head to read and write data to the disk; insufficient fly height can cause the head to hit the disk and damage the disk or head.
Following the manufacture and gram load adjustment of the suspensions, the sliders are bonded to the flexures, typically in a manual operation, to form head suspension assemblies. The head suspension assemblies are in turn mounted to actuator arms extending from a rotating actuator shaft to form a head stack assembly. The head stack assembly is then mounted with respect to a stack of magnetic disks, with the suspensions extending between the disks.
Instruments and techniques for measuring fly heights are known. The read signal strength produced by magneto-restrictive heads is proportional to the distance between the head and magnetic disk. The fly height of magneto-restrictive heads can therefore be determined as a function of the difference in the signal strength produced by the head while sliding at low speed on the disk and operational flying position. Another method for measuring fly height involves monitoring acoustic emissions (noise levels) produced by the flying head, and correlating the acoustic emission level to fly height.
Disk drive manufacturers continue to develop smaller yet higher storage capacity drives. Storage capacity increases are obtained in part by increasing the density of the information tracks on the magnetic disks (i.e., by using narrower and/or more closely spaced tracks), and by using smaller sliders and heads. These technological advances require lower and more accurate fly heights.
Unfortunately, it is becoming increasingly difficult to obtain the required fly height tolerances using known suspensions and manufacturing procedures. Suspension gram load variations account for a significant portion of fly height variations, and are the result of a number of factors. As mentioned above, suspension gram loads will vary within manufacturing tolerances. Another factor is the stacking tolerances in the disk drive assembly. Head suspension assemblies are delicate components, and the physical handling of these components during the head bonding and drive assembly procedures can also alter the suspension gram loads. Furthermore, since the disks are tightly spaced and the suspensions extend between the disks, it is difficult to readjust the suspension gram loads and therefore the fly heights following the manufacture of the disk drive assembly.
There is, therefore, a continuing need for suspensions capable of being efficiently and accurately gram load adjusted. To be commercially viable, the suspensions must be relatively efficient to manufacture. A suspension that can be gram load adjusted in a head stack assembly, and methods for performing such gram load adjustments, would be particularly desirable.